HR: 0830h
AN: S11C-0295    [PDF]
TI: P- and S-Wave Velocities in Crustal Rocks: Evidence from Measurements and Calculations
AU: * Kern, H M
EM: kern @min.uni-kiel.de
AF: Institute of Earth Sciences, Olshausenstr. 40, Kiel, 24098 Germany
AB: Elastic anisotropy is an important property of most rocks constituting the Earth crust, and it has various sources. Most important is lattice (crystallographic) preferred orientation (LPO) due to the anisotropic properties of most rock-forming minerals and the LPO of the polycrystalline aggregates. In addition, oriented microcracks and grain shape preferred orientation (SPO) may also be of importance. Because elastic wave propagation is sensitive to cracks, elastic wave velocities travelling through a rock are higher parallel to the fractures than across them. With increasing pressure microfractures close and their contribution to elastic anisotropy diminishes. The remaining part of velocity anisotropy is nearly pressure-independent and largely caused by the LPO of the constituent minerals, such as mica and hornblende. In order to evaluate the respective contribution of the various parameters, on needs to discriminate between the two effects. This poster reports results obtained from the simultaneous measurement of P- and S-wave velocities in three orthogonal directions (up to 600 MPa and 600$\deg$C) on cube-shaped samples of metamorphic crustal rocks (amphibolites, gneisses) and investigates the relationship between crystallographic fabric, oriented cracks, shear wave splitting and shear wave polarisation. The laboratory measurements are complemented by 3D velocity calculations based on the LPOs of the rock-forming minerals (hornblende, mica). The measurements and calculations show that velocity anisotropy, shear wave splitting and shear wave polarisation are interrelated to the structural frame of the rocks (foliation, lineation). This information provides a powerful tool for the understanding and interpretation of seismic data.
DE: 8020 Mechanics
DE: 8030 Microstructures
DE: 8100 TECTONOPHYSICS
SC: Seismology [S]
MN: 2003 Fall Meeting